The present invention relates to spark ignition motor fuel compositions based on liquid hydrocarbons derived from biogenic gases that are blended with a fuel grade alcohol and a co-solvent for the liquid hydrocarbon and the alcohol, and having an anti-knock index, a heat content, and a Dry Vapor Pressure Equivalent (DVPE) effective to fuel a spark ignition internal combustion engine with minor modifications. In particular, the present invention relates to Coal Gas Liquid (CGL) or Natural Gas Liquids (NGLs)-ethanol blends in which the co-solvent is biomass-derived 2-methyltetrahydrofuran (MTHF).
A need exists for alternatives to gasoline motor fuels for spark ignition internal combustion engines. Gasoline is derived from the extracting of crude oil from oil reservoirs. Crude oil is a mixture of hydrocarbons that exist in liquid phase in underground reservoirs and remains liquid at atmospheric pressure. The refining of crude oil to create conventional gasoline involves the distillation and separation of crude oil components, gasoline being the light naptha component.
Only ten percent of the world reserves of crude oil lie in the United States, with an overwhelming majority of the remaining 90 percent located outside the boundaries, not only of the United States, but also its North American free trade partners. Over 50 percent of conventional gasoline is imported, with this number to increase steadily into the next century.
Conventional gasoline is a complex composition of over 300 chemicals, including napthas, olefins, alkenes, aromatics and other relatively volatile hydrocarbons, with or without small quantities of additives blended for use in spark ignition engines. The amount of benzene in regular gasoline can range up to 3-5 percent, and the amount of sulfur to 500 ppm. Reformulated gasoline (RPG) limits the quantity of sulfur to 330 ppm and benzene to one percent, and limits the levels of other toxic chemicals as well.
Conventional alternatives to crude oil-derived fuels such as compressed natural gas, propane and electricity require large investments in automobile modification and fuel delivery infrastructure, not to mention technological development. A need exists for an alternative fuel that provides the combustion properties of motor gasoline without requiring significant engine modification, and that can be stored and delivered like motor gasoline. In order to be an advantageous alternative for gaseous alternative fuels such as methane and propane, liquid alternative fuels should also meet all Environmental Protection Agency (EPA) requirements for "clean fuels."
CGL and NGLs have unsuitably low anti-knock indexes and have thus been under-utilized as alternatives to crude oil as hydrocarbon sources for spark ignition engine motor fuels. Attempts to overcome this deficiency have rendered these hydrocarbon streams unsuitable for use as alternative fuels.
Coal gases have long been recognized because of explosions that have occurred in the course of coal mining. This gas is considered a hazard to operations and has been vented to insure safe operation. However, such venting contributes to the increasing amounts of atmospheric methane, which is a potent greenhouse gas. C. M. Boyer, et al., U.S. EPA Air and Radiation (ANR-445) EPA/400/9-90/008. Coal gases can contain significant amounts of heavier hydrocarbons, with C.sub.2+ fractions as high as 70 percent. Rice, Hydrocarbons from Coal (American Association of Petroleum Geologists, Studies in Geology #38, 1993), p. 159.
In contrast to the sourcing of conventional gasoline, over 70 percent of the world reserves of NGLs lie in North America. Imports of NGLs into the United States constitutes less than 10 percent of domestic production. NGLs are recovered from natural gas, gas processing plants, and in some situations, from natural gas field facilities. NGLs extracted by fractionators are also included within the definition of NGLs. NGLs are defined according to the published specifications of the Gas Processors Association and the American Society for Testing and Materials (ASTM). The components of NGLs are classified according to carbon chain length as follows: ethane, propane, n-butane, isobutane and "pentane plus."
"Pentane-plus" is defined by the Gas Processors Association and the ASTM as including a mixture of hydrocarbons, mostly pentanes and heavier, extracted from natural gas and including isopentane, natural gasoline, and plant condensates. Pentanes-plus are among the lowest value NGLs. While propanes and butanes are sold to the chemical industry, pentanes-plus are typically diverted to low-added-value oil refinery streams to produce gasoline. Part of the reason why pentanes plus are not generally desirable as gasoline is because they have a low anti-knock index that detracts from its performance as a spark ignition engine motor fuel, as well as a high DVPE which would result in engine vapor lock in warm weather. One advantage of pentanes plus over the other NGLs is that it is liquid at room temperature. Therefore is the only component that can be used in useful quantities as a spark ignition engine motor fuel without significant engine or fuel tank modification.
U.S. Pat. No. 5,004,850 discloses an NGLs-based motor fuel for spark ignition engines in which natural gasoline is blended with toluene to provide a motor fuel with satisfactory anti-knock index and vapor pressure. However, toluene is an expensive, crude oil-derived aromatic hydrocarbon. It's use is severely restricted under the reformulated fuel provision of the 1990 Clean Air Act Amendments.
U.S. Pat. No. 4,806,129 discloses a fuel extender for lead-free gasoline wherein the extender consists essentially of a residue naphtha obtained as a by-product of a basic crude oil refining process, anhydrous ethanol, a stabilizing amount of a water repellant (e.g., ethyl acetate and methyl isobutyl ketone), and aromatics (e.g., benzene, toluene, and xylene). As noted above, however, certain aromatics are undesirable and their use may be restricted by law due to the damaging effects on the environment.
German DE-OS 30 16 481 discloses a fuel additive useful for solubilizing water-containing mixtures of hydrocarbons and alcohols, such as gasoline and methanol. The disclosed additive includes tetrahydrofuran and purportedly may be combined with a mixture of gasoline, methanol, and water to form a stable, clear mixture.
The United States is the world's largest producer of fuel alcohol, with less than ten percent of ethanol imported. Ethanol is a biomass-derived, octane-increasing motor fuel additive. While ethanol alone has a low vapor pressure, when blended alone with hydrocarbons, the resulting mixture has an unacceptably high rate of evaporation to be used in EPA designated ozone non-attainment areas, which include most major metropolitan areas in the United States. The vapor pressure properties of ethanol do not predominate in a blend with pentanes plus until the ethanol level exceeds 60 percent by volume. However, blends containing such a high level of ethanol are costly and difficult to start in cold weather because of the high heat of vaporization of ethanol. Furthermore, ethanol has a low heat content, resulting in low fuel economy compared to gasoline.
Low-coast production of MTHF and the production and use of biomass-derived materials such as ethanol or MTHF as gasoline extenders at levels up to about ten percent by volume is disclosed by Wallington et al., Environ. Sci. Technol., 24, 1596-99 (1990); Rudolph et al., Biomass, 16, 33-49 (1988); and Lucas et al., SAE Technical Paper Series, No. 932675 (1993). Low-cost production of MTHF and its suitability as a low-octane oxygenate for addition to gasoline with or without ethanol to produce an oxygenated motor fuel are disclosed in an unpublished presentation to the Governors' Ethanol Coalition by Stephen W. Fitzpatrick, Ph.D., of Biofine, Inc. on Feb. 16, 1995. Accurate technical data involving the blending DVPE and blending octane values for MTHF were not available. There remains a need for a motor fuel having a DVPE and anti-knock index suitable for use in a spark ignition internal combustion engine without significant modification obtained from non-crude oil sources.